1. Field of the Invention
The present application relates to apparatus for sampling and analysis of analytes in a liquid sample. A liquid sample is pre-concentrated using a chromatographic column prior to analysis via a two stage analysis apparatus. A high-performance liquid chromatography system with ultra violet detection may be used in conjunction with electrochemical detection for the analysis of environmental contaminants, including explosive residues. The present invention also provides for on-site analysis of such contaminants. The present invention also provides for methods of analyzing the components of a liquid sample, including methods for on-site analysis.
2. Background of the Invention
Many environmental contaminants, including explosive residues, are known toxins and carcinogens, thus posing a threat to living species (J. Yinon, Toxicity and Metabolism of Explosives, CRC Press, Inc., Boca Raton (1990)). Current methodology for determining environmental contaminants is not always sensitive enough for trace analysis or selective enough for analysis in complex matrices. Presently, site assessment is typically done by collecting soil and ground water samples, storing them, and shipping them to specialty laboratories for analysis (J. Yinon and S. Zitrin, Modern Methods and Applications in Analysis of Explosives, John Wiley & Sons, LTD., New York, N.Y. (1993)). However explosive residues degrade over time, which can lead to inaccurate results when analyzing samples.
Several detectors have been coupled to high-performance liquid chromatography (HPLC) for the determination of explosive residues, including the ultra violet (UV) detectors, refractive index (RI) detectors, mass spectrometry (MS), and reductive dc amperometry. (J. Yinon and S. Zitrin, Modern Methods and Applications in Analysis of Explosives, John Wiley & Sons, Inc., New York (1993); A. M. Krstulovic and P. R. Brown, Reversed-Phase High-Performance Liquid Chromatography. Theory, Practice, and Biomedical Applications, John Wiley & Sons, Inc., New York, (1982); D. A. Martens and W. T. Frankenberger, Jr., Chromatographia 30:11-12 (1990); I. S. Krull, C. Selavka, and X-D. Ding, Proceedings of the International Symposium and the Analysis and Detection of Explosives, Federal Bureau of Investigation (FBI) Academy, Quantico, Mar. 29-31, 1983; A. Hilmi, et al., J. Chromatogr. A 844:97 (1999)). Both RI and UV detectors suffer from lack of sensitivity and selectivity due to the presence of interfering compounds in complex matrices. MS is complex, making it difficult to use it for performing quantitative work. Reductive amperometric techniques suffer from lack of sensitivity due to the reduction of dissolved oxygen present in the mobile phase and sample. In contrast, photo-assisted electrochemical detection (PAED) is very sensitive and selective and does not face the same limitations as reductive amperometry. HPLC-PAED involves first the separation of the analytes of interest, followed by the photolytic generation of a new species that can then be detected electrochemically (I. S. Krull, and W. R. LaCourse, Reaction Detection in Liquid Chromatography, Marcel Dekker, Inc., New York (1986)).
There exists therefore a need for a sampling system that can be used to analyze environmental liquid samples, including on-site analysis of liquid samples that would not require large sample volumes, or transportation of samples that can lead to degradation. The present application fulfills this need.